title: Early category-specific cortical activation revealed by visual stimulus inversion.
abstract: Visual categorization may already start within the first 100-ms after stimulus onset, in contrast with the long-held view that during this early stage all complex stimuli are processed equally and that category-specific cortical activation occurs only at later stages. The neural basis of this proposed early stage of high-level analysis is however poorly understood. To address this question we used magnetoencephalography and anatomically-constrained distributed source modeling to monitor brain activity with millisecond-resolution while subjects performed an orientation task on the upright and upside-down presented images of three different stimulus categories: faces, houses and bodies. Significant inversion effects were found for all three stimulus categories between 70-100-ms after picture onset with a highly category-specific cortical distribution. Differential responses between upright and inverted faces were found in well-established face-selective areas of the inferior occipital cortex and right fusiform gyrus. In addition, early category-specific inversion effects were found well beyond visual areas. Our results provide the first direct evidence that category-specific processing in high-level category-sensitive cortical areas already takes place within the first 100-ms of visual processing, significantly earlier than previously thought, and suggests the existence of fast category-specific neocortical routes in the human brain.
authors.affiliation: Cognitive and Affective Neuroscience Laboratory, Tilburg University, Tilburg, The Netherlands.
authors.forename: Hanneke K M
authors.initials: HK
authors.lastname: Meeren
authors.forename: Nouchine
authors.initials: N
authors.lastname: Hadjikhani
authors.forename: Seppo P
authors.initials: SP
authors.lastname: Ahlfors
authors.forename: Matti S
authors.initials: MS
authors.lastname: Hämäläinen
authors.forename: Beatrice
authors.initials: B
authors.lastname: de Gelder
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D009434:Neural Pathways / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology; D055815:Young Adult